1. Field of the Invention
The present invention relates to novel pigment pastes suitable for use in cationic electrodeposition, and also relates to the method of cationic electrodeposition employing paints containing the novel pigment paste.
2. Brief Description of the Prior Art
In the formation of paint compositions, and especially electrodepositable paint compositions, an important factor is the introduction of pigments into the coating composition. The pigments are typically ground in a pigment grinding vehicle which acts as a dispersing agent to form a paste, and the resultant pigment paste is incorporated into the coating composition to give the coating composition proper color, opacity, application and film properties. Unfortunately, many of the pigment pastes for electrodeposition are mixtures of water-soluble soaps or resins which are not electrodepositable. These pastes remain in the aqueous phase where they pose serious effluent problems.
The present invention overcomes this problem by providing a pigment paste containing a pigment grinding vehicle which is electrodepositable and codeposits with the vehicle resin of the paint. In addition, the grinding vehicle contains blocked isocyanate groups which are capable of unblocking at room or elevated temperatures and reacting with active hydrogens which are contained in the pigment grinding vehicle or in the main resin vehicle for electrodeposition. This results in an increase in crosslink density of the electrodeposited coating and for improved detergent and corrosion resistance.